Foam for secondary and tertiary recovery

ABSTRACT

Oil is moved in a subterranean oil-bearing formation by displacing the oil with a foamed oil-external micellar dispersion. The micellar dispersion, before foaming, contains 2 90 percent by volume hydrocarbon, at least about 4 percent by volume surfactant, about 5 - 90 percent by volume aqueous medium, and optionally 0.01 - 20 percent by volume cosurfactant and/or 0.0001 - 5 percent by weight electrolyte. Useful gases for foaming the dispersion include air, natural gas, nitrogen, flue gases, etc. The dispersion can be foamed before it is injected into the formation or it can be foamed in situ of the formation. A mobility buffer fluid and/or drive fluid may be used to displace the foam toward a production well to recover crude oil therethrough.

United States Patent I 91 7 Gogarty 5] Sept. 18, 1973 [54] FOAM FORSECONDARY AND TERTIARY 3,406,754 10/1968 Gogarty 166/273 RECOVERY. v i75 I 7 i C m 7 FT Primary Examiner-Stephen J. Novosad [m finventor I 1mm B ogarty, itt eton Co 0 yf ph C Herring-ct at [73] Assignee: MarathonOil Company, Findlay, v

. I {57 ABSTRACT 2 Filed' J 1971 7 Oil is moved in a subterraneanoil-bearing formation by [2]] Appl- N0.1 156,553' displacing the oilwith a foamed oil-external micellar dispersion. The micellar dispersion,before foaming, tains 2 90 percent by volume hydrocarbon, at 521 vs. c1166/273, 166/274 ,3 3

- 1 least about 4 percent by volume surfactant, about 5 [51] Int. ClE2lb 43/22 90 ercentb volumea ueous medium ando tionall 62-2 ,0,30R Y[58] of Search l 73 75 5 0.01, 20 percent by volume cosurfactant and/or[56] References Cited. 0.0001 5 percent by weight electrolyte. Usefulgases for foaming the dispersioninclude air,tnatural gas, ni- 3 254 714PATENTS H 1.66/2 g f n, flue gases, :tc. Thehdistpersion can be foamebdt e ore it is injecte into t e ormation 'orit' 'can. e 3: 9/ 1966 5166/274 foamed in situ of the formation. A mobilitybufferfluid 3' '83:gga f f f' and/or drive fluid may be used to displace the foam to-3269460 8/1966 Hardy et'aL 166/274 ward a production well to "recovercrude oil there- 3,529,663 9/1970 Bemardn 166/273 thmugh- 3,648,7723/1972 Earlougher/Jr. 166/273 i 3,500,919 3/1970 Holm 166/273 26 ClamsDrawmgs FOAM FOR SECONDARY AND TERTIARY RECOVERY CROSS REFERENCE TORELATED APPLICATIONS U.S. Pat. application Ser. No. 12,457, titled Useof Surfactant Foam for Recovery of Petroleum, filed 2/18/70, teaches theuse of foamed water-external micellar dispersions to recover crude oilfrom subterranean formations.

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates to secondary recovery processes (including tertiary, etc.) ofoil from subterranean oil-bearing formations. More specifically, foamedoil-external micellar dispersions comprised of hydrocarbon, surfactant,and aqueous medium are injected into and displaced through theformation. The micellar dispersion is foamed in situ, in the well bore,or on the surface.

Description of the Prior Art Foam flooding is a recognized method torecover crude oil from subterranean formations. Disadvantages of priorart, foam flooding processes are (l) unattractive oil recoveries, (2)foam tends to degrade or lose its physical characteristics as it isdisplaced through the formation, (3) lack of mobility control behind thefoam, etc.

U.S. Pat. No. 2,866,507 to Bond et al teaches oil recovery by injectingand displacing through a reservoir a foam formed by injecting gas intoan aqueous solution containing a water-soluble foaming agent.

U.S. Pat. No. 3,177,939 to Holm et al teaches a foam flooding process bythe sequential injection of (1) aqueous solution containing asurfactant, (2) a foamproducing gas, (3) a C C hydrocarbon and (4) analcohol.

U.S. Pat. No. 3,196,944 to Bernard et al teaches a foam flooding processusing a mixture of C or lower hydrocarbon along with an oil-solublefoaming agent.

U.S. Pat. No. 3,318,379 to Bond et al teaches in situ formation of afoam by first injecting a hydrocarbon mixture containing a surfactant,followed by a surfactant-free non-gaseous liquid miscible with the firstinjected slug and then injecting a gas which causes the first slug tofoam.

U.S. Pat. No. 3,530,943 to 'Dauben et al teaches forming a foam in anearth formation by using a filmforming water-soluble polymer in anaqueous foaming solution. The polymer tends to stabilize the foamagainst the adverse effects of high temperatures. Examples of polymersinclude polyvinyl alcohols and polyvinyl pyrrolidones.

SUMMARY OF THE INVENTION Applicant has discovered a method of displacingcrude oil from subterranean formations using a foamed oil-externalmicellar dispersion. Foaming of the micellar dispersion can beaccomplished on the surface, in the well bore and in situ of theformation. Optionally, the foamed micellar dispersion can be displacedby a mobility buffer fluid and/or a drive fluid. The micellar dispersioncontains aqueous medium, hydrocarbon, surfactant, and optionallycosurfactant and/or electrolyte. Examples of gases useful to foam thedispersion include air, natural gas, combustion products of natural gas,nitrogen, etc.

PREFERRED EMBODIMENTS OF THE INVENTION The micellar dispersion of thisinvention is oilexternal. It is comprised of hydrocarbon, aqueousmedium, surfactant, and optionally cosurfactant and/or electrolyte. Theoil-external micellar dispersion is foamed with any gas compatible withthe micellar dispersion components as well as the subterraneanformation. The micellar dispersion can be foamed in situ, on thesurface, or while the dispersion is being injected through the injectionmeans into the oil-bearing formation.

The hydrocarbon within the micellar dispersion can be crude oil, apartially refined fraction of crude oil (crude column overheads, gasoils, kerosene, naphthas, straight run gasoline, liquefied petroleumgases, etc.), refined fractions of crude oil (e.g. pentane, heptane,etc.) or synthesized hydrocarbons (including halogenated hydrocarbons,hydrocarbons having groups substituted on the hydrocarbon'molecule toimpart desired characteristics), etc. Examples of surfactants includethose defined in U.S. Pat. No. 3,254,714 to Gogarty et al; preferablythe surfactant is a petroleum sulfonate having an average equivalentweight within the range of about 350 to about 525, more preferably about390 to about 470. The petroleum sulfonate is preferably a mono-valentcation containing sulfonate. The aqueous medium can be soft, brackish orbrine water; but, where the water contains ions,-the ions are preferablycompatible with the ions within the subterranean formation. Thecosurfactant can be an alcohol, amine, ester, aldehyde, ketone, ether,or like compound containing one to about 20 carbon atoms. Theelectrolyte can be an inorganic salt, inorganic base, inorganic acid, orsimilar organic compounds. Examples of volume amounts include about 2 toabout percent hydrocarbon, at least about 4 percent surfactant, about 5to about :90 percent aqueous medium, about 0.001 to about 20 percentcosurfactant, and about 0.001 to about 5 percent by weight ofelectrolyte. Specific examples of useful components with this inventioncan be foundin U.S. Pat. Nos. 3,254,714, to Gogarty et al; 3,275,075 toGogarty et al; 3,330,343 to Tosch et al; and 3,497,006 to Jones et al.

The foam is obtained by intimately contacting the oilexternal micellardispersion with a compatible gas. Examples of gases compatible in a'majority of reservoirs include air, nitrogen, natural gas, combustionproducts of natural gas (also referred to as flue gases), carbondioxide, low molecular weight hydrocarbons, carbon monoxide, oxygen,mixtures of the above and like materials. The gas is preferably in asubstantially gaseous state at reservoir conditions, i.e., reservoirtemperature and pressure.

The foam may be generated on the surface and then injected through or bythe injection means into the for mation. Also, the foam may be generatedin the well bore, e.g. while the micellar dispersion and gas areprogressing down theinjection means into the formation; this can beaccomplished by alternately pumping micellar dispersion and gas into theinjection means or mixing the two via nozzles in the well bore. Anothermethod is to inject the micellar dispersion and gas simultaneously inseparate tubing strings wherein the outlets are positioned to permitgeneration of the foam downhole. In addition, the foam can be generatedin situ, e.g. the dispersion can be injected into the formation followedby a sufficient amount of gas to'foam the previously injected micellardispersion. Also, alternate slugs of micellar dispersion and gas can beinjected into the formation to form the foam in situ.

Where the foam is generated in situ, preferably about 0.1-20 percentformation pore volume of liquid micellar dispersion is injected alongwith sufficient volumes of the gas to foam the micellar dispersion.Where the foamed micellar dispersion is injected into the reservoir,preferably about 0.5 to about 40 percent and more preferably about 5 toabout 20 percent formation pore volume of the foam is injected. Where itis desired to stimulate the injection well, minimum amounts of thefoamed micellar dispersion are preferably injected; e.g. about 0.1 toabout barrels of micellar dispersion per vertical foot of oil-bearingformation are injected followed by sufficient volumes of gas to foam atleast 20 percent of the dispersion or this equivalent volume ofdispersion can be foamed and then injected into the formation.

It may be desirable to generate the foam in situ of the formation at apoint removed from the wellbore. This is accomplished by injecting anddisplacing the micellar dispersion within the formation at the desiredlocation and then injecting through another injection means, thefoam-producing gas so it will come in contact with the micellardispersion and foam the dispersion.

Volumes of gas useful to foam the oilexternal micellar dispersioninclude about 0.5 to about 30 or more and preferably about 5 to aboutvolumes of gas per volume of micellar dispersion, the volumes of gasbased on reservoir temperature and pressure. Too much gas may producewhat is called a dry foam and allow gas breakthrough during the floodingprocess, thus adversely influencing the recovery.

The foamed oil-external micellar dispersion may be displaced through thereservoir by a drive fluid or a combination mobility buffer fluid and adrive fluid.

Examples of useful drive fluids include water, thickened water, brine,LPG (liquefied petroleum gas), natural gas, air, oxygen, nitrogen,methane, combustion products of natural gas, and like materials. Wateris the preferred drive material where the foamed micellar dispersion isfollowed by a mobility buffer fluid. When the mobility buffer fluid isnot used, air or natural gas is the preferred drive material. Any drivematerial which is compatible with the reservoir and the foamed micellardispersion is' useful. Sufficient amounts of the drive fluid areinjected to displace the foamed micellar dispersion toward the producingwell.

Where a mobility buffer fluid is used, the foamed micellar dispersion isfirst injected followed by the mobility buffer fluid and then a drivefluid is used to displace the first two slugs toward the producing well.Examples of useful mobility buffer fluids include any aqueous ornonaqueous fluid containing a mobility reducing agent which effectivelyreduces the mobility of the fluid; the purpose is to impart a favorablemobility control for efficient oil recovery. Specific examples ofmobility buffer fluids include water containing mobility reducing agentssuch as partially hydrolyzed, high molecular weight polyacrylamides,polysaccharides, polyethylene oxides, carboxymethyl cellulose,carboxyvinyl polymers, polyethylene glycol, biopolymers, etc. Also, the

mobility buffer fluid can be a hydrocarbon containing a mobilityreducing agent such as polyisobutylene and other high molecular weighthydrocarbon agents. Any mobility reducing agent is useful as long as theagent effectively'reduces the mobility of the mobility buffer fluidwhile the fluid flows in the reservoir and is compatible within thereservoir.

Examples of volume amounts of useful mobility buffer fluids includeabout 5 to about 80 percent, preferably about 20 to 70 percent formationpore volume. The mobility buffer fluid can be graded from a low mobilityat the juncture of the foamed micellar dispersion and mobility bufferfluid to a high mobility at the rear end of the mobility buffer fluid,e.g. a high mobility approaching that of the mobility of a subsequentlyinjected drive fluid.

The foamed micellar dispersion, mobility buffer fluid, and drive fluidcan contain other additives to impart desired characteristics in theformation. For example, bactericides, oxygen scavenging agents, etc. maybe incorporated.

In certain cases it may be desired to foam only the back portion of theinjected oil-external micellar dispersion. With this invention, at least20 percent of the micellar dispersion is foamed to obtain efficient oilrecovery.

The following examples are presented to teach specific workingembodiments of the invention. Unless otherwise specified, all percentsare based on volume.

EXAMPLE I A rectangular, plexiglass container having inside dimensionsof 1% inches wide, 4 inches high, and 6 feet long is filled with 48 tomesh sand; permeability of the sand pack is 43 darcies and porosity is40 percent. The sand is first flooded with an aqueous solutioncontaining 2 percent sodium chloride. Thereafter, oil is flowed throughthe sandpack until residual water saturation is reached, this valueabout 31 percent. About l0 percent formation pore volume of a micellardispersion composed of 10 percent ammonium petroleum sulfonate, 2percent primary amyl alcohol, 50 percent water and the residue crude oil(viscositY of the oil is about 7 cp. at ambient temperature) is injectedinto the sand pack. Thereafter, air is injected to foam the micellardispersion and todisplace the foam through the sand pack. About 62percent of the oil is recovered from the sand pack by the foamedmicellar dispersion.

EXAMPLE I] The procedure of Example I is repeated except 15 percentformation pore volume of the oil-external micellar dispersion isinjected and sufficient quantities of air are injected thereafter tofoam the micellar dispersion. In this example, 71 percent of the oil isrecovered from the sand pack.

EXAMPLE III The procedure of Example I is duplicated except the sandpack is flooded with water after being flooded with the oil, to reducethe sand pack to residual oil saturation, i.e. now the sand pack is in atertiary condition. About 10 percent formation pore volume of theoilexternal micellar dispersion is injected and thereafter sufficientvolumes of air are injected to foam the micellar dispersion. 79 percentof the oil is recovered from the tertiary conditioned sand pack.

EXAMPLE IV The procedure of Example I is duplicated except the sand packis flooded with water, after being flooded with oil, to reduce the oilsaturation to residual oil saturation, i.e. a tertiary condition.Thereafter, 15 percent formation pore volume of the micellar dispersionis injected followed by a sufficient volume of air to foam the micellardispersion and displace the foam through the sand pack. About 83 percentof the oil is recovered from the sand pack.-

EXAMPLE V A consolidated sandstone core is first saturated with water,then flooded with oil to residual water saturation and is then floodedwith water to residual oil saturation. Thereafter, the equivalent of 2.5percent formation pore volume of an oil-external micellar dispersion(composed of 24 percent water, 10.5 percent petroleum sulfonate, 3.8percent isopropyl alcohol, and the residue straight run gasoline) isfoamed with approximately five volumes, based on the volume of themicellar dispersion, of natural gas. The foamed micellar dispersion isthen injected into the sandstone core and this, in turn, followed by amobility buffer slug composed of water containing partially hydrolyzed,high molecular weight polyacrylamide. Sufficient amounts of the mobilitybuffer are injected to displace the micellar dispersion through thecore. Economically attractive quantities of oil are recovered from thecore.

The above specific embodiments are not meant to restrict the invention.Rather, all equivalents obvious to those skilled in the art are intendedto be incorporated within the scope of the invention as defined withinthe specification and appended claims.

What is claimed is:

l. A process for recovering oil from an oil-bearing subterraneanformation having an injection means in fluid communication with aproduction means, the process comprising:

1. displacing a foam through the oil-bearing formation toward theproduction means, the foam obtained by foaming at least about 20 percentby'volume of an oil-external micellar dispersion with a foam-producinggas compatible with the micellar dispersion, and j e 2. recovering crudeoil through said production means.

2. The process of claim 1 wherein the foam is produced in thesubterranean formation by contacting the micellar dispersion with thefoam-producing gas.

3. The process of claim 1 wherein the foam is produced at the surfaceand then injected into the subterranean formation.

4. The process of claim 1 wherein the micellar dispersion is comprisedof hydrocarbon, aqueous medium and surfactant.

5. The process of claim 4 wherein the micellar dispersion containscosurfactant or electrolyte or cosurfactant and electrolyte.

6. The process of claim] wherein the foamed micellar dispersion isdisplaced through the subterranean formation by injecting a drive fluidinto the formation.

7. The process of claim 6 wherein the drive fluid is a gas.

8. The process of claim 1 wherein the foamed micellar dispersion isdisplaced through the formation by injecting a mobility buffer fluidbehind the foamed micellar dispersion and thereafter injecting a drivefluid to displace the foamed micellar dispersion and mobility bufferfluid toward the production means.

9. The process of claim 8 wherein about 5 to about 80 percent formationpore volume of the mobility buffer fluid is injected.

10. The process of claim 1 wherein about 0.5 to about 30 volumes of thefoam producing gas is used to foam the oil-external micellar dispersion,the volume of gas based on the volume of the micellar dispersion.

11. The process of claim 1 wherein the micellar dispersion is comprisedof about 2 to about 90 percent by volume hydrocarbon, about 5 to about90 percent by volume aqueous medium, and at least about 4 percent byvolume of surfactant.

12. The process of claim 1 wherein the foam is produced in the well boreof the injection means and is then injected into the formation.

13. A process for recovering crude oil from an oilbearing subterraneanformation having at least one injection means in fluid communicationwith at least one production means, the process comprising: I

l. injecting into the formation about 0.5 to about 20 percent formationpore volume of an oil-external micellar dispersion comprised of about 2to about 90 percent by volume hydrocarbon, about 5 to about 90 percentby volume aqueous medium, at least about 4 percent of a petroleumsulfonate, and

2. injecting sufficient volumes of a foam-producing gas during theinjection of the micellar dispersion to foam at least about 20 percentof the injected oil-external micellar dispersion, the foamproducing gasbeing compatible with the micellar dispersion and the subterraneanformation, and

3. thereafter displacing the foamed micellar dispersion toward theproduction means to recover crude oil therethrough.

14. The process of claim 13 wherein about 5 to about 80 percentformation pore volume of a mobility buffer fluid is injected behind thefoamed micellar dispersion.

15. The process of claim 13 wherein a water drive is injected behind thefoamed micellar dispersion to displace it toward the production means.

16. The process of claim 14. wherein the mobility buffer fluid is anaqueous solution containing a mobility reducing agent.

17. A process for recovering crude. oil from an oilbearing subterraneanformation having at least one injection means in fluid communicationwith at least one production means, the process comprising:

l. injecting a foamed oil-external micellar dispersion into theformation, the volume of the micellar dispersion before foamingequivalent to 0.5 to about 20 percent formation pore volume and themicellar dispersion comprised of about 2 to about 90 percent by volumehydrocarbon, about 5 to about 90 percent by volume aqueous medium, andat'least about 4 percent of a petroleum sulfonate, and

2. thereafter injecting into the formation about 5 to about percentformation pore volume of a mobility buffer fluid, and then 3. injectingsufficient amounts of a drive fluid to displace the foamed micellardispersion and mobility buffer fluid toward the production means torecover crude oil therethrough.

- gas.

23. A process for increasing the injectivity of injection wells in fluidcommunication with an oil-bearing subterranean formation, the processcomprising injecting into the formation the equivalent of about 0.1 toabout 10 barrels per vertical foot of oil-bearing formation of anoil-external micellar dispersion wherein at least 20 percent of themicellar dispersion is foamed with a foam-producing gas compatible withthe dispersion and displacing it out into the formation.

24. The process of claim 23 wherein at least a portion of the micellardispersion is foamed in situ of the formation.

25. The process of claim 23 wherein the micellar dispersion issubstantially foamed before it enters the formation.

26. The process of claim 23 wherein the foamed micellar dispersion isdisplaced into the formation by a water drive.

2. thereafter injecting into the formation about 5 to about 80 percentformation pore volume of a mobility buffer fluid, and then
 2. injectingsufficient volumes of a foam-producing gas during the injection of themicellar dispersion to foam at least about 20 percent of the injectedoil-external micellar dispersion, the foam-producing gas beingcompatible with the micellar dispersion and the subterranean formation,and
 2. The process of claim 1 wherein the foam is produced in thesubterranean formation by contacting the micellar dispersion with thefoam-producing gas.
 2. recovering crude oil through said productionmeans.
 3. The process of claim 1 wherein the foam is produced at thesurface and then injected into the subterranean formation.
 3. thereafterdisplacing the foamed micellar dispersion toward the production means torecover crude oil therethrough.
 3. injecting sufficient amounts of adrive fluid to displace the foamed micellar dispersion and mobilitybuffer fluid toward the production means to recover crude oiltherethrough.
 4. The process of claim 1 wherein the micellar dispersionis comprised of hydrocarbon, aqueous medium and surfactant.
 5. Theprocess of claim 4 wherein the micellar dispersion contains cosurfactantor electrolyte or cosurfactant and electrolyte.
 6. The process of claim1 wherein the foamed micellar dispersion is displaced through thesubterranean formation by injecting a drive fluid into the formation. 7.The process of claim 6 wherein the drive fluid is a gas.
 8. The processof claim 1 wherein the foamed micellar dispersion is displaced throughthe formation by injecting a mobility buffer fluid behind the foamedmicellar dispersion and thereafter injecting a drive fluid to displacethe foamed micellar dispersion and mobility buffer fluid toward theproduction means.
 9. The process of claim 8 wherein about 5 to about 80percent formation pore volume of the mobility buffer fluid is injected.10. The process of claim 1 wherein about 0.5 to about 30 volumes of thefoam producing gas is used to foam the oil-external micellar dispersion,the volume of gas based on the volume of the micellar dispersion. 11.The process of claim 1 wherein the micellar dispersion is comprised ofabout 2 to about 90 percent by volume hydrocarbon, about 5 to about 90percent by volume aqueous medium, and at least about 4 percent by volumeof surfactant.
 12. The process of claim 1 wherein the foam is producedin the well bore of the injection means and is then injected into theformation.
 13. A process for recovering crude oil from an oil-bearingsubterranean formation having at least one injection means in fluidcommunication with at least one production means, the processcomprising:
 14. ThE process of claim 13 wherein about 5 to about 80percent formation pore volume of a mobility buffer fluid is injectedbehind the foamed micellar dispersion.
 15. The process of claim 13wherein a water drive is injected behind the foamed micellar dispersionto displace it toward the production means.
 16. The process of claim 14wherein the mobility buffer fluid is an aqueous solution containing amobility reducing agent.
 17. A process for recovering crude oil from anoil-bearing subterranean formation having at least one injection meansin fluid communication with at least one production means, the processcomprising:
 18. The process of claim 17 wherein the mobility bufferfluid is an aqueous solution containing a partially hydrolyzed, highmolecular weight polyacrylamide.
 19. The process of claim 17 whereindrive water is injected to displace the foamed micellar dispersion andmobility buffer fluid toward the production means.
 20. The process ofclaim 17 wherein the micellar dispersion is foamed with air.
 21. Theprocess of claim 17 wherein the micellar dispersion is foamed withnatural gas.
 22. The process of claim 17 wherein the micellar dispersionis foamed with combustion products of natural gas.
 23. A process forincreasing the injectivity of injection wells in fluid communicationwith an oil-bearing subterranean formation, the process comprisinginjecting into the formation the equivalent of about 0.1 to about 10barrels per vertical foot of oil-bearing formation of an oil-externalmicellar dispersion wherein at least 20 percent of the micellardispersion is foamed with a foam-producing gas compatible with thedispersion and displacing it out into the formation.
 24. The process ofclaim 23 wherein at least a portion of the micellar dispersion is foamedin situ of the formation.
 25. The process of claim 23 wherein themicellar dispersion is substantially foamed before it enters theformation.
 26. The process of claim 23 wherein the foamed micellardispersion is displaced into the formation by a water drive.